Was wondering if anyone has been running LR 4.2 Beta to process their RX100 RAW images? Do you convert the images in 4.2 and go back to 4.1 to edit? Or is 4.2 stable enough to complete the editing, and final printing? [...]

It's a RC (Release Candidate). It means that it's stable enough for everyday use. It's not a beta.It overwritten my 4.1 and works flawlessly for me since then.

Just saw this filter adapter (threaded ring is attached to front of lens with double-sided tape). Filters I don't care so much about, but this would let me use a lens hood, which I do care about. Of course, and attached lens hood destroys the compact form factor of the camera (somewhat). http://www.youtube.com/watch?v=pNv6IXJZ3xI

What happens is that exposure is actually reduced. So if a certain patch would see 1000 photons at 1/4s it would only see 666 photons at 1/6s. From photon statistics, SNR would be 31.6 at 1/4s and 25.8 at 1/6s. That is physics, nothing software can do anything about. The JPEG processing pipeline probably does some noise reduction and sharpening (among many other things) and will take ISO setting into account.

Thanks for the research. DR is more important to me that noise on the RX100, so I always have shot at 125 assuming that's what will give me the most DR. What could you tell about where the DR "sweet spot" is from the tests you ran?